China’s latest lunar mission began in the early hours of December 8, 2018, when a Long March-3B carrier rocket launched from the Xichang Satellite Launch Center in southwest China’s Sichuan Province, carrying the Chang’e 4 spacecraft.
Four days later, the rocket entered lunar orbit. To facilitate the communication experiment, according to Digital Journal, China launched Queqiao, a satellite with a 4.2-meter parabolic antenna on May 20 from Xichang. The satellite entered a Lissajous orbit June 14 beyond the moon around the Earth-moon Lagrange point 2.
This orbit will allow Queqiao to be in a constant line-of-sight with both the lunar far side and terrestrial tracking stations. Queqiao will relay telecommands from the ground to the Chang’e 4 lunar spacecraft and transmit data and telemetry back to Earth via S-band while using X-band to communicate with the lander and rover.
Possible lunar landing imminent
China’s space agency said its control center in Beijing would choose a suitable time to try the landing. But the Smithsonian Institution, the American museums and research centers group, is reporting that the landing is expected to take place in a day or two.
The Von Kármán crater landing point is in an unexplored region of the far side of the Moon called the South Pole-Aitken Basin. It is a vast basin in the southern hemisphere of the far side which extends from the South Pole to Aitken crater.
Because a soft landing on the far side can be extremely challenging, mission control will rely on Queqiao or Magpie Bridge, to relay signals to the lunar lander and rover of Chang’e 4.
As for its geological composition, the crater contains about 10 percent by weight iron oxide (FeO) and four to five parts per million of thorium, which has been used as a replacement for uranium as nuclear fuel on several thorium reactors.
The Far Side
“Relative to the near side, in many respects we know very little about the far side,” said Mark Robinson, a planetary scientist at Arizona State University and the principal investigator for NASA’s Lunar Reconnaissance Orbiter Camera (LROC), reports Space.com.
Robinson and other space scientists are hoping Chang’e 4 will land near an elusive “mare” region on the far side. Mares are large, dark, basaltic plains on Earth’s Moon, formed by ancient volcanic eruptions. They cover about 16 percent of the lunar surface and most of them are on the side facing Earth.
They were dubbed maria, Latin for “seas.” They are less reflective than the “highlands” as a result of their iron-rich composition, and hence appear dark to the naked eye. “We do not have a documented sample of a farside mare, so this would be the first look,” Robinson told Scientific American.
The mare basalt represents scientist’s best look at the moon’s overall composition and its mantle, the layer between the core and crust. So if China’s rover and lander can create a detailed characterization of a mare on the far side, it could help in understanding why the two sides of the moon are so different.
After Chang’e 4 lands, the LROC camera system aboard NASA’s Lunar Reconnaissance Orbiter should be able to clearly spot the Chinese spacecraft after touchdown. “We should be able to identify the lander and rover tracks if not the rover itself,” Robinson said.
